In recent years, a fuel cell system that utilizes as its energy source a fuel cell that generates power from the electrochemical reaction between reactant gases of fuel gas and oxidizing gas has been developed. In order to improve fuel efficiency, during low-load operations, such as idling, low-speed running, braking, etc., this type of fuel cell system performs an intermittent operation where power generation by the fuel cell is temporarily stopped and power is supplied to a load (e.g., vehicle motor) from a power storage means such as a secondary battery. When the reactant gases stop being supplied to stop the fuel cell operation during the above intermittent operation, the fuel cell goes into a high-voltage state. As the fuel cell deteriorates if it is left in a high-voltage state, it is necessary to prevent the fuel cell from going into a high-voltage state, for example, by decreasing its voltage, when stopping the fuel cell operation. In the fuel cell system disclosed in Patent Document 1 indicated below, a high-voltage state is prevented by only supplying a fuel cell with fuel gas after the stoppage of the fuel cell operation, so as to consume the oxidizing gas that remains in the fuel cell and output an electric current from the fuel cell.
Patent Document 1: Japanese laid-open patent publication No. 2005-100820